1. Field of the Invention
The invention relates to an installation for continuous manufacturing of an ultrathin metal foil by electrolytic deposition.
2. Description of the Background Art
The technique of electrolytic deposition is known. It has been long employed to form thin metallic coatings on substrates of very diverse types. Continuous application is particularly useful for elongated products such as long strips, wires, filaments, fibers, or the like, which can be passed through the depositing apparatus. The technique allows production of:
adhering coatings which are permanently affixed to the substrate surface, as well as,
non-adhering coatings, which can be detached from the substrate as independent products.
In the context of this disclosure, "fabrication of an ultrathin foil" should be understood to mean formation of a non-adhering coating in the form of an ultrathin foil forming an independent product.
In the past, it has been proposed to use a mobile substrate comprised of a rotating drum which forms the cathode of the electrolysis system and which turns while faced by an anode of appropriate configuration. The electrolyte can be circulated at high speed tangentially to the cathode in the narrow space between the anode and cathode. With this arrangement, current densities of an order of 30 A/dm.sup.2 can be achieved.
Luxembourg Patent No. 86.ll9, held by the present applicant, discloses an apparatus which enables an electrolytic coating, particularly a non-adhering coating, to be applied on a rotating cathode. The apparatus has an anode designed to assure high turbulence of the electrolyte in the space between the anode and cathode, wherewith electrolyte is fed perpendicularly to the plane of the cathode. At the same time, excessive motive pressures are avoided. However, the apparatus of the cited Luxembourg Patent does not enable attainment of the high production levels required in industry.
The problem of devising a high speed apparatus stems particularly from the continuous nature of the process and the complexity of the techniques.
The mean thickness and width of the desired ultrathin foil will be based on the need of the user. For a given installation, these dimensions will vary between relatively narrow limits.
To increase the production rate, it is necessary to increase the speed of the substrate, and therefore generally the length of the deposition apparatus in order to maintain the same duration of deposition.
To some extent, the space required by the apparatus can be minimized by certain measures such as the use of an anode which allows higher current densities, and the employment of maximum current density and maximum throughput rate of electrolyte. There is still some increase in the length of the deposition zone that is necessary. This is the length of the zone where the electrodes essentially face each other. This increase is obtained by a simultaneous increase of the length of the anode and cathode in the direction of passage of the substrate. The length of the anode can be increased readily by juxtaposing a plurality of devices, as described in Luxembourg Patent No. 86.119.
Regarding the rotating drum-type cathode mentioned above, the desired increase in the length of the deposition zone requires the diameter of the drum to be substantially increased. However, in practice, this diameter is limited by considerations of fabrication, installation, and available space.
A solution might be to employ a plurality of apparatuses in series. However, serious drawbacks are attendant upon this. The foil leaving an intermediate apparatus is thinner than the final ultrathin foil. Any manipulation of it would increase the risk of tearing the product. Further, a thin foil below a "minimum thickness for detachability" cannot be detached from one drum, to pass to another. Accordingly, a limitation is placed on the speed of delivery of the foil. Finally, having multiple deposition apparatuses increases the cost and complexity of the installation by a substantial amount.
It is also known to employ a mobile cathode comprised of an endless metal belt passing over and rotating in a loop around two parallel rolls. Such a belt may have sufficient length that only one belt is required to enable completion of the entire deposition, even at high belt speed. This solves the problem presented by the above-mentioned drawbacks of rotating-drum cathode, but gives rise to other difficulties, particularly with regard to the length and speed of the belt. In particular, one might mention the difficulty of guiding a very long belt and the need to compensate for the catenary deformation of the suspended span. These difficulties are further complicated by the aggressive character of the ambient medium. Such an installation is also subject to problems of sealing and problems of retardation of the belt, the latter due to the fact that electricity is supplied to the belt by brushes.
The underlying problem solved by the present invention is to devise an installation for continuous manufacturing of an ultrathin foil by electrolyte deposition of a non-adhering coating onto a moving substrate, followed by removal of the coating, wherewith the inventive installation enables the various above-mentioned disadvantages to be avoided while assuring a high production rate of ultrathin foil.